The more leeks, onions, chives or garlic that men eat, the less likely they are to develop prostate cancer. Epidemiologists at the China-Japan Friendship Hospital in Beijing discovered the prostate-cancer inhibiting properties of the Allium vegetable family when they gathered and reanalysed data from 9 big epidemiological studies. They looked at data on 132,192 men in total.

Garlic

Not all of the studies that the Chinese used revealed equally strong protective effects of the Allium family. In some studies the protective effect was almost nil. But the overall effect – shown in the diamond in the figure below – was an 18 percent reduction in the likelihood of developing prostate cancer when Allium vegetables were present in the diet.

When the researchers separated the different categories they discovered that of all the Allium family it was garlic – yes garlic is a vegetable – that had the strongest protective effect. The table above shows this.

Diallylsulphide

Allium vegetables, and garlic in particular, contain the compound shown here on the right: diallylsulphide. A precursor of diallylsulphide is allicin, an anticatabolic substance, which has recently triggered the interest to sports scientists. [Eur J Appl Physiol. 2008 Jun;103(3):275-83.]

Researchers also suspect that diallylsulphide can inhibit the growth of cancer cells. In 2012 Korean researchers published the results of an in-vitro study [Int J Mol Sci. 2012 Nov 2;13(11):14158-71.] in which they exposed prostate cancer cells to diallylsulphide. The substance inhibited the growth of the cancer cells and even caused them to self-destruct.

How diallylsulphide is capable of killing prostate cancer cells is shown below on the left: it induces the cancer cells to produce more Death Receptor 4 [DR 4]. This receptor enables cytokines to kill cancer cells.

The figure below right shows at least one consequence of an increase in the number of death receptors: the cancer cells synthesise less of the anti-suicide protein BCL-2.

Conclusion
"Allium vegetables, especially garlic intake, are related with a low incidence of prostate cancer", the Chinese epidemiologists conclude. "Because of the limited number of studies, further well-designed cohort or intervention studies are warranted to confirm the findings from our study."